OOA training question --does yoke O-ring leak when air supply turned off ?

[scubafanatic]

When diving a yoke style 1st stage, and practicing and out-of-air emergency drill, what happens to the 'air-tightness' of the O-ring seal between the tank valve and the 1st-stage-inlet-port?

The reason I ask is it's common during training for instructors turn off a student's air supply to experience an OOA emergency, yet at the same time divers are warned how important it is to 'barely' tighten (2 fingers tight) the 1st stage yoke screw, as the air-pressure from the tank --when the tank is turned on--will 'inflate' the O-ring, bridge/seal the 'gap' and form a tight seal so water won't enter the 1st stage.

What hasn't been addressed is what happens to the 'quality' of this 'seal' when the air-pressure falls to 'zero' as the air is turned off.......will the O-ring spring a leak, allowing water into the 1st stage?

Is the 'solution' to tighten the yoke screw a bit more tightly than the recommended '2-finger-tight' level to compensate for the absence of air-pressure maintaining the o-ring seal?

Karl

 

[Scubaroo]

The seal remains when the air is turned off - that's why you have to fully purge your second stage before you can remove the yoke from the valve. There is no need for additional tightening of the yoke. Also, if you are still doing your Open Water course, ask your instructor about DIN valves and regulators if they haven't been covered yet - they are a much more secure alternative to yoke.

 

[scubafanatic]

Thanks bengiddins......but a follow-up point/question:

During my OOA 'training' , all the students had their backs to the instructors......and they randomly shut off our air supplies, without advance warning...they didn't want us 'preparing' for them.........they had us breathing normally .....so, of course, I sucked all the air that remained inside the 1st stage/hose.....maybe half-a-breath's worth of air......thus I essentially duplicated the same complete emptying of air you describe as happening when you purge the 2nd stage.....I just breathed it away versus purging it away.

It sounds like you're confirming my fears about what happens to a yoke-O-ring seal when the air pressure drops to zero......the seal 'breaks' and water enters.

Sounds like I need to tighten the yoke screw a bit past the traditional '2-finger-tightness' afterall.

I'm familiar with DIN valves/regulators....but they're not that common in the US......and I've already bought Faber yoke valve LP 120's. One of them does have a modular OMS yoke/DIN valve......but then I'd have to switch my regs over to DIN 1st stages.

I was hoping not to have to do that, but now I'm thinking more seriously about that option......I couldn't care less about going to DIN for high-pressure reasons, (I prefer to dive my overfillable LP 120 steels).....but do appreciate the much more secure connection between the 1st stage and tank valve that DIN offers.

Karl

 

[Scubaroo]

Moving to DIN is preferable to over tightening yoke regulators - especially as you own your own regulator and tanks. An over tightened yoke connection can be almost impossible to remove, even with the pressure bled out of the hoses. Try it at home with a full tank on a non-diving day and you'll see what I mean, or just take my word for it and save your hand from a world of hurt trying to undo the connection.

I wouldn't worry about the seal breaking at the o-ring when you breath down the regulator anyway - ambient pressure will retain the seal.

 

[MikeFerrara]

The seal of a yoke does not depend on the presure in the tank. The seal is provided by the o-ring. If you overtighten the connection you can damage the 0-ring causing a leak. The fact that the reg is very hard to remove with the air turned on only shows that the presure increases the strength of the mechanical connection; it has nothing to do with the integrity of the seal. A DIN is more reliable and they are plenty common here in the US. I use DIN only and I believe yoke should die a quick quite death.

Turning the students air off is a common practice in training. We don't suprise the student, however. I have them watch the gauge while they breath down the remaining presure. When they signal OOA I turn it back on. I don't just rely on theeir signal. I position myself where I can see the gauge also. This also prevents cheating (signaling before presure goes down).

 

[The Chairman]

If there were any gap at the O-RIng, it would extrude under the pressure. NO NEED TO OVERTIGHTEN ANY O-RING CONNECTION. This applies to DIN as well as Yoke. The vaccuum you could possibly produce would be miniscule. There is no benefit of DIN over Yoke in this respect.